The freshwater pearl mussel (Margaritifera margaritifera) is one of the most endangered animals in Europe, with fewer than 200 viable populations remaining globally. UK rivers hold some of the world most significant remaining colonies.
While the capacity of bivalves to experience suffering remains scientifically uncertain, the ecological role of freshwater pearl mussels in filtering river water — a single mussel can filter up to 50 litres per day — has profound welfare implications for all species dependent on clean rivers, including salmon and trout. The welfare case for protecting pearl mussel habitat is therefore indirect but substantial. Captive breeding programmes, which hold larvae on host fish under carefully controlled conditions, raise welfare questions about fish handling and stress. Best practice involves minimising handling duration and ensuring water quality matches source rivers.